The invention relates to a bipolar medical instrument for cutting tissue under the action of high-frequency current.
The invention further relates to an electrosurgical system, comprising a high-frequency generator and an instrument of the type indicated above.
An instrument and a system of the type mentioned at the outset are used in open surgery, but preferably in minimally invasive surgery, for cutting tissue in the human or animal body.
In the context of the present invention, the instrument mentioned at the outset, when used in minimally invasive surgery, can be combined with an endoscope to form what is known as a resectoscope, or it can itself constitute such a resectoscope.
Electrosurgery, or high-frequency surgery, is employed therapeutically in various medical specialties, for example in urology, gynecology, neurosurgery, abdominal surgery, etc. In urology in particular, prostate tissue is removed endoscopically in minimally invasive surgery by means of an instrument of the type mentioned at the outset.
In electrosurgical resectoscopy, a distinction is made between monopolar and bipolar application of high-frequency current.
In monopolar application, only the active electrode is introduced into the treatment region, while the neutral electrode is arranged externally on the patient. Consequently, the current flow between the active electrode and the neutral electrode passes through the patient's body, the disadvantage being that the current path through the patient cannot be safely controlled, the result of which is the possibility of damage to the organs. In addition, the neutral electrode placed on the patient's body may cause burning of the patient's skin.
In the bipolar technique, on which the present invention is based, the active electrode and the neutral electrode are both introduced into the treatment region. The current flow can in this way be limited in a controllable manner to the area between the active electrode and the neutral electrode. Accordingly, medical instruments of the type mentioned at the outset have been created in which the active electrode and the neutral electrode are arranged on an electrode carrier, in such a way that the active electrode and the neutral electrode can be introduced adjacent to one another into the treatment region.
In bipolar medical instruments of the type mentioned at the outset, the active electrode is usually configured with a small active surface area so that a high current density is created on the active electrode, whereas the neutral electrode is usually configured with a relatively large surface area so that only moderate to low current densities are created on the neutral electrode. The active electrode is accordingly used for cutting, while the neutral electrode is intended as far as possible to have no effect on the tissue and is intended simply to limit the current path to the area between the active electrode and the neutral electrode.
In the instrument known from the document DE-OS 25 21 719, the neutral electrode is configured as a tape loop, while the active electrode is configured as a wire loop. The neutral electrode is located entirely to the distal side of the active electrode and runs parallel to the latter. In this known instrument, it can happen that, when the instrument is placed on the tissue to be treated, the neutral electrode first touches the tissue, before the active electrode contacts the tissue, the result being that, when high-frequency current passes through the electrodes, the tissue in contact with the neutral electrode may possibly be cauterized, or at least damaged, even though this tissue was not to be treated. However, even upon simultaneous contact of active electrode and neutral electrode, tissue which is in contact with the neutral electrode, and which is not intended to be subjected to the effect of the high-frequency current, may be damaged.
In a further illustrative embodiment in the document DE-OS 25 21 719, the neutral electrode, on its side directed away from the active electrode, is covered by a plastic extension which is connected securely to the shaft of the resectoscope, with the result that the abovementioned problem of uninvolved tissue coming into contact with the neutral electrode is avoided. A disadvantage of this, however, is that the neutral electrode is not movable relative to the shaft of the resectoscope. In resectoscopes, however, it may be expedient to move the neutral electrode together with the active electrode relative to the shaft of the resectoscope in order to perform the cutting procedure, whereas the endoscope optical unit should be moved as little as possible, during the cutting procedure, so as not to alter the viewing angle or field of view during cutting, and thus achieve the greatest possible precision in the visual monitoring of the cutting procedure. In addition, in this illustrative embodiment, the neutral electrode is arranged to the proximal side of the active electrode, or it extends both to the proximal side and to the distal side of the active electrode.
Moreover, EP 1 163 886 A2 discloses a resectoscope instrument in which the active electrode and the neutral electrode are electrically separated on their mutually facing sides by an insulating body, such that each straight line of connection between the electrodes passes through the insulating body. This is intended to ensure that the direct current flow between the two electrodes is made difficult or is reduced, as a result of which a greater proportion of the power fed into the instrument will pass from the active electrode into the body tissue and there deploy a cutting action. In this instrument, the insulating body is arranged on the inner face of the neutral electrode directed towards the active electrode and, when the neutral electrode changes position, said insulating body can accordingly move along with it.
None of the known instruments has as yet proven satisfactory in terms of its cutting action.